This invention relates generally to vacuum-actuated test fixtures, and in particular, to a vacuum-actuated test fixture for testing individual electronic components.
There are numerous methods and test fixtures for testing the functionality of printed circuit boards and components on such boards, ranging from "bed of nails" testers to devices which clip on over a component such as an integrated circuit. However, conventional methods become more difficult to apply as boards and components thereon become physically smaller. Particularly, with the advent of surface-mounted integrated circuits and other miniaturized packages, such as microprocessors, programmable logic arrays, and other pin grid array packages, clip-on fixtures become difficult, if not impossible, to use because signal pins or component leads are not accessible on the component side of the board.
There have been various types of mechanical arrangements for clamping or holding down circuit boards proposed; however, early investigators in the art determined that the use of vacuum-actuated test fixtures provided an effective method of holding a circuit board while probing circuit nodes on the underside. Such conventional vacuum-actuated test fixtures typically pulled the circuit board assembly down onto the test pins, or probes, causing non-uniformly distributed point loads which result in undue stress, board warpage, and often damage to the circuit board.
Another problem associated with prior art vacuum-actuated test fixtures is alignment of the board with the test probes. Some test fixtures use a double-plate approach in which a set of test probes arranged in a predetermined pattern are placed into a lower plate, while the upper plate is provided with so-called tooling pins to mate with holes in the circuit board assembly to permit registration of circuit test nodes with probes. Another solution to the alignment problem is the use of a so-called universal test fixture in which the bottom plate includes a matrix of test probes, and the top plate is drilled in a predetermined pattern to mask off the unwanted probes while allowing the desired probe pins to pass therethrough to the circuit test nodes of the circuit board assembly. These fixturing techniques are expensive to implement and maintain, and require custom test heads or plates for each circuit board assembly.